Modulator



Mar. 27, 1923.

- 1,449,878. E. AUSTIN.

MODULATOR.

FILED JAN-12,1922

Fig. I.

Inventor:

Edward Austin,

Hi s Att, orhe g.

Patented Mar. 27, 1923.

UNITED STATES PATENT OFFICE.

EDWARD AUSTIN, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRICCOMPANY, A CORPORATION OF NEW YORK.

MODULATOR.

Application filed January 12, 1922. Serial No. 528,846.

To all whom it may concern:

Be it known that I, EDWARD AUsTIN, a citizen of the United States,residing at Schenectady, in the county of Schenectady,

State of New York, have invented certain new and useful Improvements inModulators, of which the following is a specification. 5

My present invention relates to modulators of high freqiiency current,and more particularly to modulators of the type commonly known asmagnetic amplifiers.

Devices of this general type as used in. the past and as described, forexample, in United States patent to Alexanderson, 1,206,643, havedepended for their action upon the varying inductance of a windingsupplied with high frequency current under variations in themagnetization of a core of magnetic material with which the winding isassociated.

When such a device has its high frequency windings connected in serieswith the antenna of a radio transmitting system the effect, if operatedin accordance with past practice is to vary the tuning of the antenna.In case a source of high frequency current such a vacuum tube generatoris employed, the frequency of which is largely determined by the antennatuning, this results in a wide change in the wave length transmittedwithout any appreciable control of the amplitude of the radiated waves.For radio telephony, however, particularly with short wave lengths, itis regarded as better practice to maintain the wave length constant andeffect the transmission by varying the amplitude of or modulating theantenna current in accordance with the telephone current.

The object of my invention is to provide a magnetic modulator which willserve to gontrol the amplitude of the antenna current withoutappreciably varying the tuning of the antenna.

In carrying my invention into effect I provide a core of magneticmaterial having two magnetizing coils surrounding two legs of apreferably closed core of magnetic material. I surround these two coilsby a winding made up of two portions wound in opposite directions. Byarranging the winding for the high frequency current in this way theinductance of the winding is greatly reduced and becomes only a smallportion of the total inductance of the oscillating circuit. Hence smallvariations in the inductance of the winding with changes in themagnetization of the magnetic core produce such small percentage changesin the total inductance of the circuit that they do not appreciablyaffect the tuning. .The high frequency losses in the core, however, varygreatly with variations in the magnetization and as a result the deviceacts principally as a variable resistance in the antenna circuit.

' The novel features which I believe'to be characteristic of myinvention are set forth with particularity in theappended claims. Myinvention itself, however, both as to its organization and method ofoperation will best be understood by reference to the followingdescription taken in connection with the accompanying drawing in whichFig. 1 shows diagrammatically the application of my invention to a radiotelephone transmitting system, and Fig. 2 is a view of the modulatorwith a portion of the windings broken away.

As indicated in the drawing, my improved modulator comprises a pair ofcoils 1 and 2 surrounding the two legs 3 and 4 of a continuous magneticcore made of thin laminations. Surrounding the coils 1 and 2 is awinding made up of two portions 5 and 6 wound in opposite directions.The winding 5, 6 is connected in series with a radiating antenna 7 whichis supplied with high frequency current from a source 8 through theusual coupling transformer 9. The source 8 may be of any form desired,either a high frequency altern ator,'an arc generator, or a vacuum tubegenerator. Modulation of the antenna current is effected by supplying atelephone current by means of the transmitter 10 and local battery 11 tothe windings 1 and 2.

While it is possible to vary the antenna current by varying the tuningthe control which is obtained in this way over the range necessary for,;efi'ecting satisfactory voice modulation of the antenna current isnonlinear. Such control therefore induces dis tortion in'the currenttransmitted and this distortion is increased by the non-linear detuningeffect of the receiver. In the case of short wave radio transmitters theinductance of the circuit being comparatively low, a

small change in the inductance of the modulator will produceconsiderable dlstortlon if the inductance of the modulator QO L- tutesan appreciable percentage of the total inductance of the oscillatingcircuit. By the arrangement which I have described it will be apparentthat the inductance of the modulator may be made to represent a verysmall percentage of the total inductance of the circuit. The modulatingeffect, however, will not be appreciably reduced since the individualfields are established. by the two halves of the high frequency winding,thus making it possible to vary the effective resistance of the windingby varying the permeability of the core. The resultant high frequencyfield, however, which determines the inductance will be very low and theper centage change in this inductance by reason of changes in themagnetization of the core will also be lower by reason of thedifferential winding. Hence for a large change in the magnetizingcurrent the percentage change in the total oscillating circuit.inductance will be very low and the distortion will be reduced to aminimum.

What I claim as new and desire to secure by Letters Patent of the UnitedStates,

1. The combination in a modulator of a closed core of magnetic materialhaving two subtantially parallel legs, winding on each of said legs anda winding surrounding the windings on both of said legs, saidlast-mentioned winding being composed of two portions wound in oppositedirections.

2. The combination in a modulating system of a closed core ofl magneticmaterial having two substantially parallel legs, windings on each ofsaid legs, means for supplying a modulating current to said windings, awinding surrounding the windings on both of said legs, said lastmentioned winding being composed of two portions wound in oppositedirections, and means for supplying high frequency currents to said lastmentioned winding.

3. The combination in a signaling system of a closed core of magneticmaterial having two substantially parallel legs, windings on each ofsaid legs, means for supplying audio frequency signaling currents tosaid windings, a winding surrounding the windings on both of said legs,said last-mentioned winding being composed of two portions wound inopposite directions, a transmitting circuit in which the last-mentionedwindings are included and means for supplying high frequency currents tosaid transmitting circuit.

In witness whereof, I have hereunto set

